The purpose of this study is to determine the effect of chronic intermittent nocturnal hypoxia on selected hepatic drug-metabolizing enzyme systems in children with OSAS. The specific aims are to evaluate the activities of cytochrome P450 (CYP)1A2, N-acetyltransferase-2 (NAT-2), xanthine oxidase (XO)and CYP2D6 in children with OSAS and to determine the effect of OSAS treatment on the activities of these enzyme systems.